Motor vehicles may have an engine start-stop during which as engine is temporarily shut down (E-stop) in order to save fuel and reduce emissions in response to the actions of a driver of the motor vehicle. The E-stops are normally controlled by a stop-start controller and use inputs such as clutch pedal position, accelerator pedal position, brake pedal position, and the engagement state of a transmission to determine when to stop and when to restart the engine. Fast actuation of the BISG is necessary for the engine cranking operation in the case of a restart from an E-stop as engine firing may be delayed to the 2nd or 3rd top dead centre (TDC) firing. A delay in engine firing can result in a failure to launch the car (from start-stop operation) due to engine stalling.
One attempt to address restarting the engine following an E-stop is disclosed by Kataoka et al in U.S. Pat. No. 6,807,934 wherein a motor generator is used to assist with positioning the crankshaft in an optimum position for the restart. Yet another attempt to address restarting the engine following an E-stop is disclosed by Grob et al in U.S. Pat. No. 6,202,614 wherein the crankshaft is put in a predeterminable starting position via an electrical machine when an engine restart signal is received and before ignition is performed for an engine restart.
However, the inventors herein have recognized potential issues with such systems. In the approach of Kataoka et al, pre-tensioning the belt drive using the BISG is not possible. In the approach of Grob et al, the restart signal is provided as the engine is ready to start and there may be a need to wait for the engine to be positioned.
One potential approach to at least partially address some of the above issues includes a system and a method of controlling an engine of a motor vehicle comprising an engine and a belt drive wherein the belt drive is drivingly connecting a crankshaft of the engine to an integrated starter-generator. The system further comprises a least one belt tensioner for applying a tension to the belt drive. The method comprises determining whether it is desirable to perform an automatic engine stop. If it is desirable to stop the engine, the engine may be stopped. When the engine has stopped, the belt integrated starter-generator may be energized to rotate the crankshaft at low speed in the direction required for starting the engine while applying a high torque to the belt drive to pre-tension the belt drive to be ready for restarting the engine.
For example, the BISG may be rotated at a low speed after the engine has been stopped in order to pretension the drive belt and position the crankshaft of the engine in an ideal position for restarting. The BISG may be energized at a level sufficient to provide a holding torque. Thus, a robust and rapid engine start using the BISG without belt slippage and the need to increase static belt tension may be provided. In another example, the BISG may be kept energized at the holding level for a predefined period of time so as to give time for any pressure in a compressed cylinder to dissipate and then, after the predefined period of time has elapsed, the BISG is de-energized or powered down. In such a case the predefined period of time would need to be set so as to provide sufficient time for the compressed gas to dissipate.
In this way, a BISG may be used to pre-tension a FEAD belt when an engine has entered an E-stop by rotating the crankshaft slowing in the same direction required for starting the engine with the BISG operating at high torque. The rotation of the crankshaft is slow enough to prevent firing of the engine. This allows for the crankshaft to be rotated into a preferred rotational position ready for restarting the engine. Upon an engine restart, the BISG is used to drive the FEAD belt to rotate the crankshaft. Thus, a rapid restart of the engine is provided.
Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be carried out by the control system including the controller in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various actions, operations, and/or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated actions, operations and/or functions may be repeatedly performed depending on the particular strategy being used. Further, the described actions, operations and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the engine control system, where the described actions are carried out by executing the instructions in a system including the various engine hardware components in combination with the electronic controller.